Before we begin, there's one thing you need to know: The best food to eat before a workout depends on when you're going to eat it.

If you're an early riser who goes to the gym on the way to work, you won't have enough time between leaving home and arriving at the gym to really digest a full breakfast. Your pre-workout snack is going to have to be really light. On the other hand, if you're working out in the middle of the afternoon, your workout is going to be fueled by your choices at lunch and you'll have a couple of hours to digest your food before hitting the gym. That means a different pre-workout meal from the one you might choose if you were scrounging around the kitchen at 5:30 a.m. on the way to the track.

The closer to your workout, the more you want to focus on eating carbohydrates rather than fat or protein. Carbohydrates are digested in the small intestines, whereas fat and protein are broken down in the stomach. This means cramping and indigestion are more likely when you work out with a belly full of fat- or protein-rich foods.

The rule is this: The less time until the workout, the less you should eat. This makes sense: It takes time to digest food, so you don't want to scarf down a huge breakfast right before getting on the treadmill. Those planning to run the marathon on Sunday usually eat a huge dinner on Saturday night. But those planning to go for a three-mile jog at 5:30 a.m. may be fine with just an orange eaten about 20 minutes before.